IEC 15457-2-08: Technical Specifications and Compliance Guide for Flexible Insulating Sleeving Test Methods

IEC 15457‑2‑08 (formally IEC 15457‑2:2008) specifies a set of uniform methods of test for evaluating the performance of flexible insulating sleevings used in electrical equipment and systems. Originally published in 2008 and reaffirmed in 2018, this standard forms the core of qualification and quality assurance programs for sleeving materials made from textiles, polymer films, or coated fabrics. The following sections provide a detailed analysis of the scope, technical requirements, implementation highlights, and compliance notes for engineers and quality personnel.

Scope

IEC 15457‑2‑08 is applicable to flexible insulating sleevings of circular cross‑section with an inside diameter up to 80 mm, intended for electrical insulation at voltages typically up to 1 000 V rms. The standard does not define performance levels or classification; rather, it provides the test procedures that shall be used in conjunction with product‑specific standards (e.g., IEC 15457‑1) or purchaser specifications. The tests cover mechanical, electrical, and thermal properties, including:

Tensile strength and elongation at break
Dielectric strength (dry and after conditioning)
Bending and flexibility under low temperature
Thermal endurance and heat shock resistance
Resistance to fluids and abrasion

The document is intended for use by manufacturers, testing laboratories, and certification bodies.

Technical Requirements

Each test method in IEC 15457‑2‑08 defines the apparatus, specimen preparation, conditioning, procedure, and calculation of results. The following subsections highlight the most critical tests.

Tensile Strength and Elongation

Specimens are cut from the sleeving to a predetermined length (typically 200 mm between grips) and pulled at a constant rate of (250 ± 50) mm/min. The tensile strength is calculated as the maximum force divided by the cross‑sectional area of the sleeving wall. Elongation is expressed as the percentage increase in initial length at break. The standard requires a minimum of five test results for statistical validity.

Dielectric Strength

The dielectric strength test is performed on a 300 mm length of sleeving placed between two metal electrodes. A 50 Hz alternating voltage is raised at a uniform rate until breakdown occurs. Both dry specimens and specimens conditioned in a controlled humidity environment (23 °C / 50 % RH for 24 h) are tested. The result is recorded in kV/mm of wall thickness. Table 1 summarises typical test parameters.

Table 1 — Summary of key test conditions from IEC 15457‑2‑08
Property	Test Condition	Reporting Unit	Required Number of Specimens
Tensile strength (Type A)	250 mm/min, 23 °C, 50 % RH	MPa	5
Elongation at break	same as above	%	5
Dielectric strength (dry)	500 V/s rise, 23 °C, <30 % RH	kV/mm	5
Dielectric strength (wet)	24 h at 23 °C / 95 % RH	kV/mm	5
Heat shock	200 °C ± 2 °C for 1 h	Pass / Fail (no cracking)	3
Low‑temperature flexibility	‑40 °C ± 2 °C, 4 h	Pass / Fail (no cracking)	3

Thermal Endurance and Heat Shock

The heat shock test exposes a 300 mm sleeving specimen to (200 ± 2) °C in an air‑circulating oven for 1 h. After removal and cooling to room temperature, the sleeving is inspected for cracks, splits, or any visible deterioration. For thermal endurance assessment, the standard references the procedure in IEC 60216‑2 (Arrhenius extrapolation), but does not prescribe specific temperatures or lifetimes.

Tip: When performing dielectric strength tests, ensure the electrode edges are rounded to avoid corona discharge. Pre‑conditioning at the specified humidity is critical for repeatable results; deviations of more than ± 5 % RH may significantly alter the breakdown voltage for hygroscopic sleevings.

Implementation Highlights

Testing in accordance with IEC 15457‑2‑08 requires the laboratory to possess calibrated tensile test machines with a resolution of ± 1 N, dielectric test sets with a voltage rise rate controlled to within ± 10 %, and temperature chambers capable of maintaining ± 2 °C throughout the working volume. Key implementation steps include:

Specimen preparation: Cut sleeving to length in a single, clean cut. Remove any dust or loose fibres.
Conditioning: Follow the standard’s mandatory conditioning period of 24 h at (23 ± 2) °C and (50 ± 10) % RH before any mechanical test.
Environmental control: For dielectric tests that require a “dry” condition, the relative humidity in the test area shall be below 30 % during the measurement.
Data recording: All individual readings, mean values, and standard deviations shall be reported. Outliers must be identified and treated according to ISO 5725‑2.

Warning: The tensile test can generate high forces; use appropriate safety guards. For sleevings containing glass fibre, wear respiratory protection when cutting specimens to avoid inhaling airborne fibres.

Good practice: Many laboratories perform a preliminary “break‑in” cycle on a dummy sample to verify that the test rig and sensors are operating correctly before measuring the actual batch. This reduces the risk of losing meaningful data due to equipment malfunction.

Compliance Notes

IEC 15457‑2‑08 is a horizontal standard; it does not by itself confer compliance of a product. To claim compliance with a particular performance grade (e.g., class A, B, or C as per IEC 15457‑1), the manufacturer must ensure that the sleeving passes all the applicable tests specified in the product standard. Key compliance considerations include:

Batch testing: For each production lot, at least the tensile strength, elongation, and dielectric strength (dry) shall be tested. If the sleeving is intended for low‑temperature applications, the low‑temperature flexibility test must also be included.
Certificate of conformity: The test report shall state the standard designation (IEC 15457‑2‑08) and all the individual test results. It must also list the conditioning parameters and any deviations from the standard procedure.
Accreditation: Laboratories performing these tests should be accredited according to ISO/IEC 17025. Accreditation provides confidence that the methods are correctly implemented and the results are traceable to SI units.
Market surveillance: Regulatory authorities may request evidence of compliance. Retaining test records for at least five years is strongly recommended.

Important: Failure to strictly follow the conditioning and rate‑of‑strain requirements can lead to invalid results. For example, testing at a grip separation speed of 300 mm/min instead of 250 mm/min may increase the apparent tensile strength by 5–10 % for elastomeric sleevings, giving a falsely optimistic assessment.

Frequently Asked Questions

Q: What is the relationship between IEC 15457‑2‑08 and the newer IEC 15457‑2:2018?
A: IEC 15457‑2‑08 (the 2008 edition) was reaffirmed in 2018 without technical changes, so the two designations are functionally identical. The 2018 reaffirmation simply confirmed the continued validity of the test methods. All current compliance certifications may reference either edition.

Q: Can I use these test methods for sleeving with a non‑circular cross‑section?
A: No. IEC 15457‑2‑08 is limited to circular cross‑section sleevings. For rectangular or flat sleevings, alternative methods (e.g., IEC 60674‑3‑2) should be consulted.

Q: What is the minimum number of specimens required for the dielectric strength test?
A: The standard requires five valid dielectric breakdown readings for each condition (dry, conditioned, etc.). If a specimen breaks down at the electrode edge rather than within the test area, that result must be discarded and replaced.

Q: Does the standard cover testing of assembled wire harnesses?
A: No. IEC 15457‑2‑08 applies only to bare sleeving before assembly. For testing after harness fabrication, refer to the appropriate system‑level standard, such as IEC 62368‑1 or the relevant product specification.

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